Cushioning device for rock drills



, Feb. 8, 1944. M. O FARRELL Y 2,341,472

V CUSHIONI'NG DEVICE FOR ROCK DRILLS Filed Jan. 21. 1942 2 Sheets-Sheet l ATTORNEY Feb; 8, l1944. M. OEARRELL 2,341,472

CUSHONING DEVICE nFORROCK DRILLS Filed'Jan. 2 1, 1942 2 sheets-sheet 2 Patented Felo. 8, 1944 CUSHIONING DEVICE FOR ROCK DRLLS Matthew OFarrell, Detroit, Mich., assigner to Chicago Pneumatic Tool Company, New York,

N. Y., a corporation of New Jersey Application'lanuary 21, 1942, Serial No. 427,582

' 1 Claim. ,(01. 255-51) This invention relates to rock drilling mechanism and more particularly to a cushioning device for a rock drill of the type that is fed toward and from the work by a motor driven feed screw.

In the operation of drilling apparatus of this type it frequently happens, through inadvertence; that the motor feed is permitted to continue turning the feed screw at the end of the backward stroke of the drill with the result that the motor stalls only after the drill has struck a stationary part of the support. The reaction of the impact may produce a tight locking engagement between the feed screw and feed nut and prevent the motor from starting on its next forward stroke.

The general object of the invention is to cushion the impact of the drill at the end of its rearward stroke thereby permitting the motor to stall before the axial thrust against the Vfeed nut becomes excessive.

More specific objects are the provision of a bulfer spring constructed and arranged to present a gradually increasing resistance to axial movement of the drill and, hence, to rotation of the feed screw; to enclose such a spring for the purposes of protecting the operator against injury and excluding muck from the spring; and

to support the spring out of contact With thev feed screw.

In the accompanying drawings which illustrate one embodiment of the invention:

Fig. 1 is a side elevation of a drilling mechanism equipped with the cushioning arrangement of the present invention;

Fig. 2 is a plan View of a fragmentary portion of the drilling mechanism shown in Fig. 1, the

rock drill and parts carried thereby being omitted I with the exception of the feed nut retainer and associated washer which are illustrated in broken lines; y

Fig. 3 is a side view, partly in elevation and partly in section, of the apparatus shown in Fig. 2, a part of the rock drill being illustrated in broken lines in the` position assumed by the drill when it rst makes Contact with the buffer spring;

Fig. 4 is a View similar to Fig. 3 but with the drill shown in full lines and in the position of maximum compression ofl the buffer spring; and

Fig. 5 is a cross section, as indicated by the arrows 5 in Fig. 3.

In the illustrative embodiment of the invention, the drilling mechanism comprises a rock drill I slidably supported by a guide shell II. Longitudinal movement of the drill on the shell is effected outer periphery and the bore 33 by a feed screw I2 having threaded engagement with a feed nut I3 xed to a projection I 4 depending from the drill. As seen rin Fig. 4, the feed nut I3 is held in place by va retaining nut I5 having screw-threaded engagement around the feed nut I3 and abutting against a washer IIB on the drill.

The feed screw I2 is driven b-y a rotary vane type air motor, not

shown, enclosed within a motor feedhousingl Il. The housing is supported by side rods I8 which pass through apertured projections onzthe guide shell II and on a buifer spring case I9 which is clamped between the rear end of the guide shelland the front end of the motor housing Il. The rotary motor is controlled by the usual throttle handle-2t and imparts rotation through a suitable gear reduction, not shown', to a driving head 2| supported in a bushing 22. Head 2I has internal splines 23 cooperating with external splines on the feed screw I2 adjacent its rear extremity.

Feed screw I2 is provided with a collar 2li confined between a thrust washer 25 and a thrust bushing 25. The bushing 26 may be mounted either rigidly or loosely in motor feed housing Il', While the washer 25 is free to float. Preferably, the washer and bushing are made of a softer metal than that of the feed screw collar 24. The front face of the thrust washer is engageable with a washer 21 which is disposed in a recess 23 in buffer spring case I9. Washer 21 abuts against the front extremity of motor housing I'I and is held against rotation by a pin 21a. Bushing 25 has a lian-ge 29 seated in a counterbore 30 in motor housing I'I. The arrangement of the bushing 26 and washers 25 and 21 permits free rotary movement of the feed screw I2 but prevents its axial movement in either a forward or a rearward direction.

Within buffer spring case IQ is a spring 32 which encircles a cylindrical portion of the feed screw I2. Preferably, the spring is of such dimensions that it has a slight clearance between ,its of the casing I9, and a somewhat greater clearance around the feed screw I2. The spring is maintained in preloaded condition or under initial compression between washer 2l and an internal flange 34 at the front extremity of buffer spring case ISI. Spring 32 acts as a buier for the retaining nut I 5 which is carried by the drill. For this purpose, the nut is provided with a cylindrical extension 3B adapted to project within the ange 34 on the spring case I9. The extension may abut against the front end of the spring and compress it during rearward movement of the drill from the Fig. 3 to the Fig. 4 position.

The operation of the illustrative embodiment of the invention is as follows. Assume that the drill is in an advanced position and the operator desires to retract it. The throttle handle 2! is turned to the reverse position and the motor feed starts to operate with the drivinghead 2I imparting rotation vto the feed screw I2 through the splines 23. Rotation of the feed screw relative to the feed nut I3 causes the drill I0 to slide in the guide shell II in a Well known manner. Ordinarily the operator will stop the feed motor at or prior to the time thatthe drill reaches the position shown in Figs. l and 3. If, however, rotation of the feed screw I2 is permitted to continue, the extension 36 on the feed nut retainer comes into contact with the buffer spring 32 as shown in Fig. 3. Further rotation of the feed screw I2 is resisted by the pressure of spring 32 which is transmitted through the feed nutretainer I5 and feed nut I3, thereby causing a part of the motor torque to beexpended in compressing the spring as well as in overcoming the fric tion between the screw threads. The pressure of the spring against the extension 36 increases gradually as the feed screw I2 continues rotating and the extent of compression of the spring increases. `By way of illustration, the spring may be placed under an initial compression of V150 pounds and increase its resistance by a like amount for each one-eighth inch of compression of the spring, while the projection 36 moves in contact with the spring for a maximum distance of vabout three-quarters of an inch. At some point in the movement of the projection against the spring pressure, the torque required to continue driving the feed screw I2 will rise to such an extent as to stall the motor and prevent further rotation of the feed screw I2.

When the operator desires to advance the drill IIJ, he turns the throttle handle to the forward position, thereby reversing the air con-v nections to the rotary motor. The torque required to turn the feed screw I2 in the forward feeding direction is less than the torque at which the motor stalled previously, and the motor starts in the usual manner, driving the feed screw I2, causing the drill I0 to carry the projection 3B out of range of the buffer spring 32 and permitting the spring to expand to the position shown inFig. 3.

The arrangement of the buffer spring 32 within the spring case I9 is such that the spring is out of contact with the feed screw I2, does not rotate with the screw, and does not exert axial'pressure against the screw. The enclosure for the spring has the additional advantages of safety for the operator and the exclusion of muck from the spring and associated working parts.

What is claimed is:

A rock drilling mechanism comprising a guide shell, a rock drill mounted for reciprocation therein, a feed nut carried by the drill, a feed nut retainer fastened around the rear extremity of the feed nut for rigidly securing the feed nut to the drill, a feed screw having threaded engagement with the feed nut for imparting reciprocatory movement to the drill, a thrust collar on the feed screw, thrust sustaining means on opposite sides of the thrust collar and carried by the guide shell-for inhibiting axial movement of the feed screw, a buffer spring surrounding the feed screw but not rotatable therewith, a spring case surrounding the buffer spring and having an internal projection at its front end to engage the front end of the spring to maintainthe spring under initial compression, said feed nut retainer having an extension adapted to bypass said internal projection upon said spring case and abut against the frontend of the spring and remove said front end of the latter from contact with said internal projection and compress the spring upon movement of the drill at the end of its rearward stroke.

MATTHEW OFARRELL. 

